1. Field of the Invention
This invention relates to an annular wear sleeve assembly installable with a low insertion force into an annular clearance space between a circular metal shaft and a surrounding annular housing to provide a smooth contact surface for an annular elastomeric seal element. The wear sleeve assembly is designed to efficiently conduct frictional heat generated between the seal element and the wear sleeve into the shaft or the housing depending on whether the wear sleeve assembly is installed on the shaft or on the housing.
2. Description of Prior Developments
Wear sleeves have been used to provide a smooth, hard contact surface for engaging an elastomeric seal lip so as to protect the seal lip from rough shaft surfaces. Some wear sleeves have been designed to conduct heat from the seal lip to a shaft. However, prior wear sleeves often required high installation forces which caused damage to the seal or resulted in improper or misaligned seal mounting which immediately or eventually resulted in seal leakage.
More particularly, when installing a wear sleeve over a shaft or into a bore, it is desirable to minimize the installation force required to overcome the frictional resistance to axial movement between the sleeve and shaft or bore. Since the wear sleeve must form a fluid tight seal with the bore or shaft, prior wear sleeve designs required the use of elastomeric liners or required a tight metal-to-metal press fit. In the case of elastomeric liners, the elastomers served as a thermal barrier to the conduction of heat from the seal lip to the shaft or bore. This condition resulted in high seal lip temperatures which led to premature seal failures as these excessive running temperatures embrittled and degraded the elastomeric lip materials causing the seal lip to lose its resilience and thus lose contact with the shaft.
In the case of press fit metal liners, very high installation forces were required and resulted in seal damage during installation. Accordingly, a need exists for a wear sleeve which efficiently conducts heat from a seal lip to a shaft or housing bore and which requires a relatively low installation force yet provides a fluid-tight seal.
Wear sleeves for elastomeric sealing elements are shown in U.S. Pat. No. 3,207,521 to R. Dega, U.S. Pat. No. 3,214,180 to Hudson, et al, U.S. Pat. No. 3,383,117 to Fagel and U.S. Pat. No. 4,552,367.
In the arrangement of U.S. Pat. No. 3,207,521 the annular wear unit has a relatively thick annular elastomeric liner molded to conform to the surface of the shaft on which the wear unit is mounted. The elastomeric liner acts as a barrier to the flow of heat from the wear unit into the shaft so that shaft cannot act as an effective heat dissipation device.
The wear sleeve structure of U.S. Pat. No. 3,214,180 includes two axially-spaced annular resilient rings located in grooves formed in the inner surface of the wear unit. These rings are sized to grip the shaft surface for operatively positioning the wear unit on the shaft. The resilient rings act as spacers between the wear unit and shaft surface thereby acting as thermal isolators so that the shaft cannot serve as a heat dissipation device.
The issue of effective heat transfer from a seal lip to a shaft is addressed in U.S. Pat. No. 3,383,117 to Fagel wherein a copper wear sleeve is covered with a layer of chromium applied by a galvanizing process. The issue of installation force is not addressed.
U.S. Pat. No. 4,552,367 shows an annular metallic wear unit that has a relatively short axially-extending section adapted to have a press fit on the surface of a shaft on which the wear unit is mounted. Another longer annular section of the wear unit has a relatively larger internal diameter that provides an annular surface spaced radially away from the shaft surface. This longer annular section of the wear unit is designed for an easy manual slip fit on the shaft, for thus piloting the wear sleeve assembly firmly onto the shaft prior to press fit interference action between the wear unit and shaft surface.
In order for the wear unit of U.S. Pat. No. 4,552,367 to be operatively installed on a shaft, the shaft diameter must be within a relatively close tolerance range relative to the internal diameter of the wear sleeve assembly. If the shaft diameter is too small the wear sleeve assembly will be loose on the shaft. If the shaft diameter is too large it will not be possible to force the wear unit onto the shaft without compromising the structural integrity of the wear unit.